Non-uniform excitation field-based method and system for performing magnetic nanoparticle imaging

ABSTRACT

The present disclosure belongs to a field of biomedical imaging technology, and in particularly to a non-uniform excitation field-based method and system for performing a magnetic nanoparticle imaging. The present disclosure includes: separating the non-uniform excitation field into independent space and current time functions by a spatialtemporal separation method; calculating a normalized signal peak through the current time function; constructing a reconstruction mathematical model based on the normalized signal peak and an imaging subunit volume; and quantitatively reconstructing a spatial distribution of a nanoparticle by combining the normalized signal peak, a non-uniform spatial function of the excitation field and the reconstruction mathematical model, so as to achieve the magnetic nanoparticle imaging of a to-be-reconstructed object.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of Chinese Patent Application No.202111125585.6 filed on Sep. 23, 2021 in the China National IntellectualProperty Administration, the content of which is incorporated herein byreference in entirety.

TECHNICAL FIELD

The present disclosure relates to a field of a biomedical imagingtechnology, and particularly to a non-uniform excitation field-basedmethod and system for performing a magnetic nanoparticle imaging.

BACKGROUND

A magnetic nanoparticle is a nanoscale particle with superparamagnetism.In recent years, the magnetic nanoparticle has been widely researchedand applied as a novel medical imaging tracer in clinical problems suchas tumor detection, magnetic particle thermotherapy, targeted drugdelivery and the like.

The method for performing a magnetic nanoparticle imaging (MPI) includescontrolling a gradient magnetic field with a high field strength to codean entire imaging field, applying a high-frequency uniform excitationfield to excite the magnetic nanoparticle to generate a nonlinearresponse, and finally performing an imaging by using a response voltagesignal detected by a receiving coil. A traditional magnetic nanoparticleimaging uses a uniform excitation field, which is intended to establisha one-to-one mapping relationship between a detection voltage signaltime sequence u(t) and a magnetic nanoparticle spatial distributionc(r). The one-to-one mapping relationship is shown in the followingequation.

${u(t)} = {{- \mu_{0}}{\int_{V}{\frac{\partial{M_{0}\left\lbrack {H_{E}\left( {r,t} \right)} \right\rbrack}}{\partial t}{p_{R}(r)}{c(r)}dV}}}$

In practice, it is very difficult to generate a wide-range uniformmagnetic field. Generally, a volume of an excitation coil needs to beincreased to acquire a larger uniform range, which may cause problemssuch as a high power consumption, a serious heat generation and thelike. At present, an existing commercial magnetic nanoparticle imagingdevice is only suitable for an imaging of a small animal, and a lengthand a width of an imaging field of view may only be about a fewcentimeters.

Therefore, in order to further promote a development of a magneticnanoparticle imaging technology to a large animal and a clinical field,a novel magnetic nanoparticle imaging method capable of overcoming alimitation of a uniform magnetic field excitation is still urgentlyrequired in the art.

SUMMARY

In order to solve the above-mentioned problem in the prior art, that is,the problem that the prior art may not overcome a limitation of theuniform magnetic field excitation, resulting in a small imaging field ofview and a limited application range of the magnetic nanoparticle, thepresent disclosure provides a non-uniform excitation field-based methodfor performing a magnetic nanoparticle imaging, including:

-   -   exciting a to-be-reconstructed object through a non-uniform        excitation field H_(E)(r, t), and performing a spatialtemporal        separation of the non-uniform excitation field H_(E)(r, t), so        as to obtain a spatial distribution A₀(r) of a non-uniform        magnetic field generated by an excitation coil and an excitation        current time-domain waveform I_(E)(t);    -   acquiring, based on the spatial distribution A₀(r) of the        non-uniform magnetic field generated by the excitation coil and        the excitation current time-domain waveform I_(E)(t), a magnetic        field space distribution p_(R)(r) generated by a receiving coil        and a magnetic nanoparticle response voltage signal u_(p)(t);    -   performing a normalization processing on the magnetic        nanoparticle response voltage signal u_(p)(t), so as to obtain a        normalized magnetic nanoparticle signal s(t);    -   performing a gridding processing on an imaging space of the        to-be-reconstructed object, so as to obtain N imaging subunits,        wherein a n-th imaging subunit has a volume ΔV_(n) and n=1, 2, .        . . , N;    -   calculating a normalized signal peak s_(p) based on the        normalized magnetic nanoparticle signal s(t), and constructing a        first mathematical model between the normalized signal peak        s_(p) and a magnetic nanoparticle spatial distribution c(r_(n))        by combining the volume ΔV_(n) of the imaging subunit; and    -   solving the first mathematical model to obtain the magnetic        nanoparticle spatial distribution c(r_(n)), so as to achieve the        magnetic nanoparticle imaging of the to-be-reconstructed object.

In some embodiments, the excitation current time-domain waveform A₀(r)of the non-uniform magnetic field generated by the excitation coil andthe magnetic field space distribution p_(R)(r) generated by thereceiving coil are acquired by one of an actual measurement method, ananalytical equation solution method or a finite element numericalsimulation method, respectively.

In some embodiments, the excitation current time-domain waveformI_(E)(t) is one of a sine wave, a cosine wave, a square wave or a pulsewave.

In some embodiments, the normalized magnetic nanoparticle signal s(t) isacquired by:s(t)=u _(p)(t)/[I _(E)(t)]^(k)

-   -   wherein k is a frequency multiplication number of the magnetic        nanoparticle response voltage signal u_(p)(t), and k is a        positive odd number.

In some embodiments, the first mathematical model between the normalizedsignal peak s_(p) and the magnetic nanoparticle spatial distributionc(r_(n)) is expressed as:

$s_{p} = {\gamma{\overset{N}{\sum\limits_{n = 1}}{\left\lbrack {A_{0}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta V_{n}}}}$

-   -   wherein A₀(r_(n)) represents a spatial distribution of a        non-uniform magnetic field generated by an excitation coil        corresponding to a n-th imaging subunit, p_(R)(r_(n)) represents        a magnetic field spatial distribution generated by a receiving        coil corresponding to the n-th imaging subunit, n=1, 2, . . . ,        N and n represents the n-th imaging subunit of N imaging        subunits, and γ represents a proportionality constant related to        a frequency of an excitation field, a magnetic moment of a        single magnetic particle and a temperature.

In another aspect of the present disclosure, there is provided aspatialtemporally coded non-uniform excitation field-based method forperforming a magnetic nanoparticle imaging, including:

-   -   generating, on the basis of exciting a to-be-reconstructed        object through a non-uniform excitation field H_(E)(r, t) of the        above-mentioned method, a gradient magnetic field with a        field-free region in an imaging space through a pair of direct        current coils in an opposite axial direction or a permanent        magnet;    -   changing a distribution of the gradient magnetic field through a        low-frequency alternating magnetic field generated by a        low-frequency alternating current coil, and driving the        field-free region to scan and traverse an entire imaging space        along a set track, so as to obtain M scanning moments and M        scanning positions;    -   acquiring a normalized signal peak s_(p)(t_(m)) at a m-th moment        thorough the above-mentioned method, wherein m=1, 2, . . . , M;    -   acquiring a voxel function ΔV(t_(m), r_(n)) of a response        voltage signal of a n-th imaging subunit at a m-th scanning        moment according to the distribution of the gradient magnetic        field and the scanned track;    -   constructing a second mathematical model between the normalized        signal peak s_(p)(t_(m)) and a magnetic nanoparticle spatial        distribution c(r_(n)) based on the normalized signal peak        s_(p)(t_(m)) at the m-th moment and the voxel function ΔV(t_(m),        r_(n)) of the response voltage signal at the m-th scanning        moment; and    -   solving the second mathematical model to obtain the magnetic        nanoparticle spatial distribution c(r_(n)), so as to achieve the        magnetic nanoparticle imaging of the to-be-reconstructed object.

In some embodiments, the second mathematical model between thenormalized signal peak s_(p)(t_(m)) and the magnetic nanoparticlespatial distribution c(r_(n)) is expressed as:

${s_{p}\left( t_{m} \right)} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta{V\left( {t_{m},r_{n}} \right)}}}}$

wherein A₀(r_(n)) represents a spatial distribution of a non-uniformmagnetic field generated by an excitation coil corresponding to a n-thimaging subunit, p_(R)(r_(n)) represents a magnetic field spatialdistribution generated by a receiving coil corresponding to the n-thimaging subunit, n=1, 2, . . . , N represents the n-th imaging subunitof N imaging subunits, and γ represents a proportionality constantrelated to a frequency of an excitation field, a magnetic moment of asingle magnetic particle and a temperature.

In a third aspect of the present disclosure, a non-uniform excitationfield of a coil array-based method for performing a magneticnanoparticle imaging is provided, including:

-   -   sequentially exciting, on the basis of exciting a        to-be-reconstructed object through a non-uniform excitation        field H_(E)(r, t) of the above-mentioned method, an imaging        space by using a plurality of excitation coils with same or        different axial directions at different positions, so as to        construct an excitation coil array;    -   simultaneously detecting a magnetic nanoparticle response        voltage signal by using a plurality of receiving coils with same        or different axial directions at different positions so as to        construct a receiving coil array, wherein the plurality of        receiving coils correspond to the plurality of excitation coils;    -   acquiring a unit current magnetic field spatial function A₀        ^(m)(r_(n)) of a m-th excitation coil and a sensitivity spatial        function p_(R) ^(l)(r_(n)) of a l-th receiving coil, acquiring a        volume ΔV_(n) of a n-th imaging subunit and n=1, 2, . . . , N,        performing a normalization of a m×1 magnetic nanoparticle        response voltage signal u_(p)(t), and acquiring a normalized        signal peak s_(p) ^(m×l) of a normalized magnetic nanoparticle        signal s(t) through the above-mentioned method;    -   constructing a third mathematical model between the normalized        signal peak s_(p) ^(m×l) and a magnetic nanoparticle spatial        distribution c(r_(n)) based on the normalized signal peak s_(p)        ^(m×l) and the volume ΔV_(n) of the imaging subunit; and    -   solving the third mathematical model to acquire the magnetic        nanoparticle spatial distribution c(r_(n)), so as to achieve the        magnetic nanoparticle imaging of the to-be-reconstructed object.

In some embodiments, the third mathematical model between the normalizedsignal peak s_(p) ^(m×l) and the magnetic nanoparticle spatialdistribution c(r_(n)) is expressed as:

$s_{p}^{m \times l} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}^{m}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}^{l}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta V_{n}}}}$

wherein A₀(r_(n)) represents a spatial distribution of a non-uniformmagnetic field generated by an excitation coil corresponding to a n-thimaging subunit, p_(R)(r_(n)) represents a magnetic field spatialdistribution generated by a receiving coil corresponding to the n-thimaging subunit, n=1, 2, . . . , N and n represents the n-th imagingsubunit of N imaging subunits, γ represents a proportionality constantrelated to a frequency of an excitation field, a magnetic moment of asingle magnetic particle and a temperature, m represents the m-thexcitation coil and l represents the l-th receiving coil.

In a fourth aspect of the present disclosure, there is provided anon-uniform excitation field-based system of performing a magneticnanoparticle imaging, including:

-   -   a first magnetic field excitation module configured to excite a        to-be-reconstructed object through a non-uniform excitation        field H_(E)(r, t);    -   a spatialtemporal separation module configured to perform a        spatialtemporal separation of the non-uniform excitation field        H_(E)(r, t), so as to obtain a spatial distribution A₀(r) of a        non-uniform magnetic field generated by an excitation coil and        an excitation current time-domain waveform I_(E)(t);    -   a magnetic field spatial distribution and response voltage        signal acquisition module configured to acquire, based on the        spatial distribution A₀(r) of the non-uniform magnetic field        generated by the excitation coil and the excitation current        time-domain waveform I_(E)(t) a magnetic field space        distribution p_(R)(r) generated by a receiving coil and a        magnetic nanoparticle response voltage signal u_(p)(t);    -   a normalization module configured to perform a normalization        processing on the magnetic nanoparticle response voltage signal        u_(p)(t), so as to obtain a normalized magnetic nanoparticle        signal s(t);    -   a gridding module configured to perform a gridding processing on        an imaging space of the to-be-reconstructed object, so as to        obtain N imaging subunits, wherein a n-th imaging subunit has a        volume ΔV_(n) and n=1, 2, . . . , N;    -   a first model construction module configured to calculate a        normalized signal peak s_(p) based on the normalized magnetic        nanoparticle signal s(t) and to construct a first mathematical        model between the normalized signal peak s_(p) and the magnetic        nanoparticle spatial distribution c(r_(n)) by combining the        volume ΔV_(n) of the imaging subunit; and    -   a first imaging module configured to solve the first        mathematical model to obtain the magnetic nanoparticle spatial        distribution c(r_(n)), so as to achieve the magnetic        nanoparticle imaging of the to-be-reconstructed object.

BRIEF DESCRIPTION OF THE DRAWINGS

The other features, objects and advantages of the present disclosurewill be clearer by reading the detailed description of non-limitingembodiments made with reference to the following accompanying drawings.

FIG. 1 shows a schematic flow diagram of a non-uniform excitationfield-based method for performing a magnetic nanoparticle imagingaccording to the present disclosure;

FIG. 2 shows a scanning track schematic diagram of a spatialtemporallycoded non-uniform excitation field-based method for performing amagnetic nanoparticle imaging according to an embodiment of the presentdisclosure;

FIG. 3 shows a coil array schematic diagram of a non-uniform excitationfield of a coil array-based method for performing a magneticnanoparticle imaging according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure will be further described in detail withreference to the accompanying drawings and examples. It may beunderstood that the specific embodiments described herein are merelyillustrative of the present disclosure and are not intended to limit thescope of the present disclosure. In addition, it should be noted that,for convenience of description, only portions related to the presentdisclosure are illustrated in the accompanying drawings.

It should be noted that, embodiments and features of the embodiments inthe present disclosure may be combined with each other without aconflict. The present disclosure will be described in detail below withreference to the accompanying drawings in conjunction with theembodiments.

In the present disclosure, a non-uniform excitation field-based methodfor performing a magnetic nanoparticle imaging is provided, including:

-   -   step S10 of exciting a to-be-reconstructed object through a        non-uniform excitation field H_(E)(r, t), and performing a        spatialtemporal separation of the non-uniform excitation field        H_(E)(r, t), so as to obtain a spatial distribution A₀(r) of a        non-uniform magnetic field generated by an excitation coil and        an excitation current time-domain waveform I_(E)(t);    -   step S20 of acquiring, based on the spatial distribution A₀(r)        of the non-uniform magnetic field generated by the excitation        coil and the excitation current time-domain waveform I_(E)(t), a        magnetic field space distribution p_(R)(r) generated by a        receiving coil and a magnetic nanoparticle response voltage        signal u_(p)(t);    -   step S30 of performing a normalization processing on the        magnetic nanoparticle response voltage signal u_(p)(t), so as to        obtain a normalized magnetic nanoparticle signal s(t);    -   step S40 of performing a gridding processing on an imaging space        of the to-be-reconstructed object, so as to obtain N imaging        subunits, wherein a n-th imaging subunit has a volume ΔV_(n) and        n=1, 2, . . . , N;    -   step S50 of calculating a normalized signal peak s_(p) based on        the normalized magnetic nanoparticle signal s(t), and        constructing a first mathematical model between the normalized        signal peak s_(p) and a magnetic nanoparticle spatial        distribution c(r_(n)) by combining the volume ΔV_(n) of the        imaging subunit; and    -   step S60 of solving the first mathematical model to obtain the        magnetic nanoparticle spatial distribution c(r_(n)), so as to        achieve the magnetic nanoparticle imaging of the        to-be-reconstructed object.

In order to more clearly describe the non-uniform excitation field-basedmethod for performing a magnetic nanoparticle imaging according to thepresent disclosure, the steps in the embodiments of the presentdisclosure will be described below in detail with reference to FIG. 1 .

In a first embodiment of the present disclosure, the non-uniformexcitation field-based method for performing a magnetic nanoparticleimaging includes step S10 to step S60. The steps are described in detailas follows.

In the step S10, a to-be-reconstructed object is excited through anon-uniform excitation field H_(E)(r, t), and a spatialtemporalseparation for the non-uniform excitation field H_(E)(r, t) isperformed, so as to obtain a spatial distribution A₀(r) of a non-uniformmagnetic field generated by an excitation coil and an excitation currenttime-domain waveform I_(E)(t).

The spatial distribution A₀(r) of the non-uniform magnetic fieldgenerated by the excitation coil and the excitation current time-domainwaveform I_(E)(t) are an independent spatial function and an independenttime function, respectively. A₀(r) may be acquired by a method such asan actual measurement method, an analytical equation solution method ora finite element numerical simulation method, etc. I_(E)(t) may bemainly generated by a signal generator and a power amplifier without alimitation on a waveform, and may be a sine wave, a cosine wave, asquare wave or a pulse wave, etc.

A relationship between the non-uniform excitation field H_(E)(r, t) andthe spatial distribution A₀(r) of the non-uniform magnetic fieldgenerated by the excitation coil and the excitation current time-domainwaveform I_(E)(t) is shown in equation (1).H _(E)(r,t)=A ₀(r)I _(E)(t)  (1)

In the step S20, a magnetic field spatial distribution p_(R)(r)generated by a receiving coil and a magnetic nanoparticle responsevoltage signal u_(p)(t) are acquired based on the spatial distributionA₀(r) of the non-uniform magnetic field generated by the excitation coiland the excitation current time-domain waveform I_(E)(t).

A sensitivity spatial function of the receiving coil, i.e., the magneticfield spatial distribution p_(R)(r) generated by the receiving coil, maybe acquired from the above-mentioned process. p_(R)(r) may also beobtained by a method such as an actual measurement method, an analyticalequation solution method or a finite element numerical simulationmethod.

An excitation current I_(E)(t) is introduced into the excitation coil togenerate a required non-uniform excitation field in an imaging space, soas to excite a magnetic nanoparticle in a space. However, a distributionof the excitation field is not limited and is determined by a geometricstructure of the excitation coil itself. The method of the presentdisclosure may be applied to any excitation coil.

In the step S30, a normalization processing is performed on the responsevoltage signal u_(p)(t) so as to obtain a normalized magneticnanoparticle signal s(t). The normalized magnetic nanoparticle signals(t) is shown in equation (2).s(t)=u _(p)(t)/[I _(E)(t)]^(k)  (2)

Where k is a frequency multiplication number of the response voltagesignal u_(p)(t) of the magnetic nanoparticle, and k is a positive oddnumber.

The response voltage signal u_(p)(t) may be a full-band signal, or maybe any odd frequency multiplication component, such as one frequencymultiplication, three frequency multiplications, five frequencymultiplications, etc. The response voltage signal u_(p)(t) may beselected according to an actual magnetic field strength and asignal-to-noise ratio. k represents the frequency multiplication numberand may be selected from 1, 3, 5, etc.

In the step S40, a gridding processing is performed on an imaging spaceof the to-be-reconstructed object, so as to obtain N imaging subunits, an-th imaging subunit has a volume ΔV_(n) and n=1, 2, . . . , N.

For different imaging spaces, the divided imaging subunits arerespectively: for a three-dimensional imaging space, the imaging subunitis a voxel; for a two-dimensional imaging space, the imaging subunit isa surface element; for a one-dimensional imaging space, the imagingsubunit is a line element.

In the step S50, a normalized signal peak s_(p) is calculated based onthe normalized magnetic nanoparticle signal s(t), and a firstmathematical model between the normalized signal peak s_(p) and themagnetic nanoparticle spatial distribution c(r_(n)) is constructed bycombining the volume ΔV_(n) of the imaging subunit. The firstmathematical model is shown in equation (3).

$\begin{matrix}{s_{p} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta V_{n}}}}} & (3)\end{matrix}$

Where A₀(r_(n)) represents a spatial distribution of a non-uniformmagnetic field generated by an excitation coil corresponding to a n-thimaging subunit, p_(R)(r_(n)) represents a magnetic field spatialdistribution generated by a receiving coil corresponding to the n-thimaging subunit, n=1, 2, . . . , N and n represents the n-th imagingsubunit of N imaging subunits, and γ represents a proportionalityconstant related to a frequency of an excitation field, a magneticmoment of a single magnetic particle and a temperature.

Presetting that the proportionality constant γ is related to thefrequency of the excitation field, the magnetic moment of the singlemagnetic particle and the temperature, when the above-mentionedparameters remain unchanged, γ is a fixed value; and when the excitationcoil, a geometry of the receive coil and a gridding mode are determined,equation parameters A₀(r_(n)) p_(R)(r_(n)) and ΔV_(n) are also uniquelydetermined. k represents a frequency multiplication number and may be 1,3, 5, etc.

In the step S60, the first mathematical model is solved to obtain themagnetic nanoparticle spatial distribution c(r_(n)), so as to achievethe magnetic nanoparticle imaging of the to-be-reconstructed object.

In order to improve an imaging accuracy and a spatial resolution, asmuch data as possible, i.e., more normalized signal peaks s_(p), need tobe acquired. The present disclosure provides both a second embodimentand a third embodiment on the basis of the first embodiment in order toincrease the number of s_(p).

In the second embodiment of the present disclosure, a spatialtemporallycoded non-uniform excitation field-based method for performing amagnetic nanoparticle imaging is provided, which includes step A10 tostep A60.

In the step A10, on the basis of exciting a to-be-reconstructed objectthrough a non-uniform excitation field H_(E)(r, t) of the non-uniformexcitation field-based method for performing a magnetic nanoparticleimaging, a pair of direct current coils in an opposite axial directionor a permanent magnet is additionally added, so as to generate agradient magnetic field with a field-free region (FFR) in an imagingspace. A magnetic nanoparticle in a region outside the FFR is in asaturation state due to a large magnetic field, and may not respond tothe excitation field.

In the step A20, a low-frequency alternating magnetic field is generatedby a low-frequency alternating current coil and a distribution of thegradient magnetic field is changed, thereby changing a position of theFFR. The FFR is driven to scan and traverse an entire imaging spacealong a specific track. Each scanning moment corresponds to a certainposition in the space, so that M scanning moments and M scanningpositions may be obtained.

In the step A30, a normalized signal peak s_(p)(t_(m)) is acquired at am-th moment through the step S10 to step S50 of the above-mentionednon-uniform excitation field-based method for performing a magneticnanoparticle imaging, where m=1, 2, . . . , M.

In the step A40, a voxel function ΔV(t_(m), r_(p)) of a response voltagesignal of a n-th imaging subunit at a m-th scanning moment is acquiredaccording to the distribution of the gradient magnetic field and thescanned track, and a volume of a voxel other than the FFR is set to bezero.

In the step A50, a second mathematical model between the normalizedsignal peak s_(p)(t_(m)) and a magnetic nanoparticle spatialdistribution c(r_(n)) is constructed based on the normalized signal peaks_(p)(t_(m)) at the m-th moment and the voxel function ΔV(t_(m), r_(n))of the response voltage signal at the m-th scanning moment. The secondmathematical model is shown in equation (4).

$\begin{matrix}{{s_{p}\left( t_{m} \right)} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta{V\left( {t_{m},r_{n}} \right)}}}}} & (4)\end{matrix}$

Where A₀(r_(n)) represents a spatial distribution of a non-uniformmagnetic field generated by an excitation coil corresponding to a n-thimaging subunit, p_(R)(r_(n)) represents a magnetic field spatialdistribution generated by a receiving coil corresponding to the n-thimaging subunit, n=1, 2, . . . , N represents the n-th imaging subunitof N imaging subunits, and γ represents a proportionality constantrelated to a frequency of an excitation field, a magnetic moment of asingle magnetic particle and a temperature.

In the step A60, the second mathematical model is solved to obtain themagnetic nanoparticle spatial distribution c(r_(n)), so as to achievethe magnetic nanoparticle imaging of the to-be-reconstructed object.

FIG. 2 shows a scanning track schematic diagram of a spatialtemporallycoded non-uniform excitation field-based method for performing amagnetic nanoparticle imaging according to an embodiment of the presentdisclosure. The FFR scans from left to right along a first line, scansfrom right to left along a second line, scans from left to right along athird line, . . . , and so on, so as to complete the scanning in anentire region. The scanning track is only one preferred track of thepresent disclosure. In other applications, other scanning tracks may beselected according to actual needs, which will not be described indetail in the present disclosure.

In the third embodiment of the present disclosure, a non-uniformexcitation field of a coil array-based method for performing a magneticnanoparticle imaging is provided, which includes step B10 to step B50.

In the step B10, on the basis of exciting a to-be-reconstructed objectthrough a non-uniform excitation field in the above-mentionednon-uniform excitation field-based method for performing a magneticnanoparticle imaging, an imaging space is sequentially excited by usinga plurality of excitation coils with same or different axial directionsat different positions so as to construct an excitation coil array.

In the step B20, a magnetic nanoparticle response voltage signal issimultaneously detected by using a plurality of receiving coils withsame or different axial directions at different positions so as toconstruct a receiving coil array, and the plurality of receiving coilscorrespond to the plurality of excitation coils.

In the step B30, through the step S10 to step S50 of the above-mentionednon-uniform excitation field-based method for performing a magneticnanoparticle imaging, a unit current magnetic field spatial function A₀^(m)(r_(n)) of a m-th excitation coil and a sensitivity spatial functionp_(R) ^(l)(r_(n)) of a l-th receiving coil is acquired, a volume ΔV_(n)of a n-th imaging subunit is acquired and n=1, 2, . . . , N, anormalization of a m×l magnetic nanoparticle response voltage signal isperformed, and a normalized signal peak s_(p) ^(m×l) of a normalizedmagnetic nanoparticle signal s(t) is acquired.

In the step B40, a third mathematical model between the normalizedsignal peak s_(p) ^(m×l) and a magnetic nanoparticle spatialdistribution c(r_(n)) is constructed based on the normalized signal peaks_(p) ^(m×l) and the volume ΔV_(n) of the imaging subunit. The thirdmathematical model is shown in equation (5).

$\begin{matrix}{s_{p}^{m \times l} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}^{m}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}^{l}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta V_{n}}}}} & (5)\end{matrix}$

Where A₀(r_(n)) represents a spatial distribution of a non-uniformmagnetic field generated by an excitation coil corresponding to a n-thimaging subunit, p_(R)(r_(n)) represents a magnetic field spatialdistribution generated by a receiving coil corresponding to the n-thimaging subunit, n=1, 2, . . . , N represents the n-th imaging subunitof N imaging subunits, γ represents a proportionality constant relatedto a frequency of an excitation field, a magnetic moment of a singlemagnetic particle and a temperature, m represents the m-th excitationcoil, and l represents the l-th receiving coil.

In the step B50, the third mathematical model is solved to obtain themagnetic nanoparticle spatial distribution, so as to achieve themagnetic nanoparticle imaging of the to-be-reconstructed object.

FIG. 3 shows a coil array schematic diagram of a non-uniform excitationfield of a coil array-based method for performing a magneticnanoparticle imaging according to an embodiment of the presentdisclosure. The coil array includes an excitation coil and a receivingcoil. A circle of coils outside an imaging region is a schematic diagramof the coil array, which indicates a presence of a plurality ofexcitation coils or receiving coils at different axes. Positions of theexcitation coils and positions of the receiving coils are notparticularly limited, and may be flexibly adjusted as needed inpractical applications, which is not described in detail in the presentdisclosure.

Although the above-mentioned embodiments have described the steps in theabove-mentioned sequence, those skilled in the art will appreciate that,in order to achieve the effect of this embodiment, different steps arenot necessarily performed in such a sequence, and may be performedsimultaneously (in parallel) or in an inverse sequence. These simplevariations are all within the scope of protection of the presentdisclosure.

In the fourth embodiment of the present disclosure, a non-uniformexcitation field-based system for performing a magnetic nanoparticleimaging is provided, and the system, based on the above-mentionednon-uniform excitation field-based method for performing a magneticnanoparticle imaging, includes:

-   -   a first magnetic field excitation module configured to excite a        to-be-reconstructed object through a non-uniform excitation        field H_(E)(r, t);    -   a spatialtemporal separation module configured to perform a        spatialtemporal separation of the non-uniform excitation field        H_(E)(r, t), so as to obtain a spatial distribution A₀(r) of a        non-uniform magnetic field generated by an excitation coil and        an excitation current time-domain waveform I_(E)(t);    -   a magnetic field spatial distribution and response voltage        signal acquisition module configured to acquire, based on the        spatial distribution A₀(r) of the non-uniform magnetic field        generated by the excitation coil and the excitation current        time-domain waveform I_(E)(t) a magnetic field space        distribution p_(R)(r) generated by a receiving coil and a        magnetic nanoparticle response voltage signal u_(p)(t);    -   a normalization module configured to perform a normalization        processing on the magnetic nanoparticle response voltage signal        u_(p)(t), so as to obtain a normalized magnetic nanoparticle        signal s(t);    -   a gridding module configured to perform a gridding processing on        an imaging space of the to-be-reconstructed object, so as to        obtain N imaging subunits, wherein a n-th imaging subunit has a        volume ΔV_(n) and n=1, 2, . . . , N;    -   a first model construction module configured to calculate a        normalized signal peak s_(p) based on the normalized magnetic        nanoparticle signal s(t) and to construct a first mathematical        model between the normalized signal peak s_(p) and the magnetic        nanoparticle spatial distribution c(r_(n)) by combining the        volume ΔV_(n) of the imaging subunit; and    -   a first imaging module configured to solve the first        mathematical model to obtain the magnetic nanoparticle spatial        distribution c(r_(n)), so as to achieve the magnetic        nanoparticle imaging of the to-be-reconstructed object.

In the fifth embodiment of the present disclosure, a spatialtemporallycoded non-uniform excitation field-based system for performing amagnetic nanoparticle imaging is provided. Based on the above-mentionednon-uniform excitation field-based method for performing a magneticnanoparticle imaging and the above-mentioned spatialtemporally codednon-uniform excitation field-based method for performing a magneticnanoparticle imaging, the system includes the following modules forperforming corresponding operations.

A second magnetic field excitation module is configured to generate, onthe basis of exciting a to-be-reconstructed object through a non-uniformexcitation field H_(E)(r, t), a gradient magnetic field with afield-free region in an imaging space through a pair of direct currentcoils in an opposite axial direction or a permanent magnet.

A scanning module is configured to change a distribution of the gradientmagnetic field through a low-frequency alternating magnetic fieldgenerated by a low-frequency alternating current coil, and to drive thefield-free region to scan and traverse an entire imaging space along aset track, so as to obtain M scanning moments and M scanning positions.

A first normalized signal peak acquisition module is configured toacquire a normalized signal peak s_(p)(t_(m)) at a m-th moment throughstep S10 to step S50 of the above-mentioned non-uniform excitationfield-based method for performing a magnetic nanoparticle imaging,wherein m=1, 2, . . . , M.

A voxel function generation module is configured to acquire a voxelfunction ΔV(t_(m), r_(n)) of a response voltage signal of a n-th imagingsubunit at a m-th scanning moment according to the distribution of thegradient magnetic field and the scanned track.

A second mathematical model construction module is configured toconstruct a second mathematical model between the normalized signal peaks_(p)(t_(m)) and a magnetic nanoparticle spatial distribution c(r_(n))based on the normalized signal peak s_(p)(t_(m)) at the m-th moment andthe voxel function ΔV(t_(m), r_(n)) of the response voltage signal atthe m-th scanning moment.

A second imaging module is configured to solve the second mathematicalmodel to obtain the magnetic nanoparticle spatial distribution c(r_(n)),so as to achieve the magnetic nanoparticle imaging of theto-be-reconstructed object.

In the sixth embodiment of the present disclosure, a non-uniformexcitation field of a coil array-based system for performing a magneticnanoparticle imaging is provided. Based on the above-mentionednon-uniform excitation field-based method for performing a magneticnanoparticle imaging and the above-mentioned non-uniform excitationfield of a coil array-based method for performing a magneticnanoparticle imaging, the system includes the following modules forperforming corresponding operations.

A third magnetic field excitation module is configured to sequentiallyexcite, on the basis of exciting a to-be-reconstructed object through anon-uniform excitation field H_(E)(r, t), an imaging space by using aplurality of excitation coils with same or different axial directions atdifferent positions so as to construct an excitation coil array, and tosimultaneously detect a magnetic nanoparticle response voltage signal byusing a plurality of receiving coils with same or different axialdirections at different positions so as to construct a receiving coilarray, and the plurality of receiving coils correspond to the pluralityof excitation coils.

A second normalized signal peak acquisition module is configured toacquire a unit current magnetic field spatial function A₀ ^(m)(r_(n)) ofa m-th excitation coil and a sensitivity spatial function p_(R)^(l)(r_(n)) of a l-th receiving coil, acquire a volume ΔV_(n), n=1, 2, .. . , N of a n-th imaging subunit, perform a normalization of a m×lmagnetic nanoparticle response voltage signal, and acquire a normalizedsignal peak s_(p) ^(m×l) of a normalized magnetic nanoparticle signals(t) through step S10 to step S50 of the above-mentioned non-uniformexcitation field-based method for performing a magnetic nanoparticleimaging.

A third mathematical model construction module is configured toconstruct a third mathematical model between the normalized signal peaks_(p) ^(m×l) and a magnetic nanoparticle spatial distribution c(r_(n))based on the normalized signal peak s_(p) ^(m×l) and the volume ΔV_(n)of the imaging subunit.

A third imaging module is configured to solve the third mathematicalmodel to obtain the magnetic nanoparticle spatial distribution c(r_(n)),so as to achieve the magnetic nanoparticle imaging of theto-be-reconstructed object.

Those skilled in the art will clearly understand that, for convenienceand simplicity of description, the specific working process and relateddescription of the above-mentioned system may be explained withreference to the corresponding process in the method embodimentdescribed above, which will not repeated here.

It should be noted that the non-uniform excitation field-based system ofperforming a magnetic nanoparticle imaging, the spatialtemporally codednon-uniform excitation field-based system of performing a magneticnanoparticle imaging and the non-uniform excitation field of a coilarray-based system of performing a magnetic nanoparticle imagingprovided in the above-mentioned embodiments are only illustrated by adivision of the above-mentioned functional modules. In practicalapplications, an allocation of the above-mentioned functions may becompleted by different functional modules as needed, that is, themodules or steps in the embodiments of the present disclosure arefurther decomposed or combined. For example, the modules in theabove-mentioned embodiments may be combined into a module, or may befurther split into a plurality of sub-modules, so as to complete all orpart of the functions described above. Names of the modules and stepsinvolved in the embodiments of the present disclosure are only todistinguish each modules or step, and are not to be regarded as animproper limitation on the present disclosure.

In the seventh embodiment of the present disclosure, there is providedan electronic device including:

-   -   at least one processor; and    -   a memory in communication with the at least one processor.

The memory has an instruction executable by the processor storedtherein, and the instruction is used to be executed by the processor soas to implement the above-mentioned non-uniform excitation field-basedmethod for performing a magnetic nanoparticle imaging, or theabove-mentioned spatialtemporally coded non-uniform excitationfield-based method for performing a magnetic nanoparticle imaging, orthe above-mentioned non-uniform excitation field of a coil array-basedmethod for performing a magnetic nanoparticle imaging.

In the eighth embodiment of the present disclosure, there is provided acomputer-readable storage medium, the computer-readable storage mediumhas a computer instruction executable by the computer so as to implementthe above-mentioned non-uniform excitation field-based method forperforming a magnetic nanoparticle imaging, or the above-mentionedspatialtemporally coded non-uniform excitation field-based method forperforming a magnetic nanoparticle imaging, or the above-mentionednon-uniform excitation field of a coil array-based method for performinga magnetic nanoparticle imaging.

Beneficial Effects of the Present Disclosure

The non-uniform excitation field-based method for performing a magneticnanoparticle imaging in the present disclosure includes: exciting themagnetic nanoparticle by using the non-uniform excitation field so as togenerate a non-uniform response voltage signal, separating thenon-uniform excitation field into an independent spatial function and acurrent time function by a spatialtemporal separation method,calculating a normalized signal peak by the current time function, andfinally quantitatively reconstructing a spatial distribution of ananoparticle by combining the normalized signal peak, a non-uniformspatial function of an excitation field and a reconstruction equation.The method of the present disclosure may solve problems such as a largepower consumption, a high maintenance cost, a difficulty in generating awide-range uniform high-frequency excitation field and the like causedby a necessary use of a uniform excitation field in a traditional methodfor performing a magnetic nanoparticle imaging. At the same time, themethod may reduce an artifact error caused by the non-uniform excitationfield, and effectively improve a precision and a resolution of an image.

Those skilled in the art will clearly understand that, for convenienceand simplicity of description, the specific working process and relateddescriptions of the storage device and the processing device describedabove may be explained with reference to the corresponding process inthe method embodiment described above, which will not repeated here.

Those skilled in the art will appreciate that modules and method stepsof each example described in conjunction with the embodiments disclosedherein may be implemented by an electronic hardware, a computersoftware, or a combinations thereof. Programs corresponding to softwaremodules and method steps may be placed in a random access memory (RAM),a memory, a read only memory (ROM), an electrically programmable ROM, anelectrically erasable programmable ROM, a register, a hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. In order to clearly illustrate an interchangeability between anelectronic hardware and an electronic software, components and steps ofeach example have been generally described above in terms of theirfunctionality. Whether these functions are performed by the electronichardware or the electronic software depends on the particularapplication and design constraint of the technical solution. Thoseskilled in the art may implement the function described above usingdifferent methods for each particular application, but suchimplementation should not be considered beyond the scope of the presentdisclosure.

The terms such as “first,” “second,” and the like are used todistinguish between similar elements and not necessarily to describe orimply a particular order or sequence.

The terms “including,” or any other variation thereof, are intended tocover a non-exclusive inclusion, so that a process, a method, an articleor a device/apparatus including a list of elements include not onlythose elements, but also other elements not expressly listed, orelements inherent to the process, the method, the article or thedevice/apparatus.

So far, the technical solution of the present disclosure has beendescribed in conjunction with the embodiments shown in the accompanyingdrawings. However, those skilled in the art may easily understand thatthe scope of protection of the present disclosure is obviously notlimited to these specific embodiments. Without departing from theprinciple of the present disclosure, those skilled in the art may makeequivalent changes or substitutions of related technical features, andthese technical solutions to be changed or substituted should all fallwithin the scope of protection of the present disclosure.

What is claimed is:
 1. A non-uniform excitation field-based method forperforming a magnetic nanoparticle imaging, comprising: exciting ato-be-reconstructed object through a non-uniform excitation fieldH_(E)(r, t), and performing a spatialtemporal separation of thenon-uniform excitation field H_(E)(r, t), so as to obtain a spatialdistribution A₀(r) of a non-uniform magnetic field generated by anexcitation coil and an excitation current time-domain waveform I_(E)(t);acquiring, based on the spatial distribution A₀(r) of the non-uniformmagnetic field generated by the excitation coil and the excitationcurrent time-domain waveform I_(E)(t), a magnetic field spacedistribution p_(R)(r) generated by a receiving coil and a magneticnanoparticle response voltage signal u_(p)(t); performing anormalization processing on the magnetic nanoparticle response voltagesignal u_(p)(t), so as to obtain a normalized magnetic nanoparticlesignal s(t); performing a gridding processing on an imaging space of theto-be-reconstructed object, so as to obtain N imaging subunits, whereina n-th imaging subunit has a volume ΔV_(n) and n=1, 2, . . . , N;calculating a normalized signal peak s_(p) based on the normalizedmagnetic nanoparticle signal s(t), and constructing a first mathematicalmodel between the normalized signal peak s_(p) and a magneticnanoparticle spatial distribution c(r_(n)) by combining the volumeΔV_(n) of the imaging subunit; and solving the first mathematical modelto obtain the magnetic nanoparticle spatial distribution c(r_(n)), so asto achieve the magnetic nanoparticle imaging of the to-be-reconstructedobject.
 2. The method according to claim 1, wherein the excitationcurrent time-domain waveform A₀(r) of the non-uniform magnetic fieldgenerated by the excitation coil and the magnetic field spacedistribution p_(R)(r) generated by the receiving coil are acquired byone of an actual measurement method, an analytical equation solutionmethod or a finite element numerical simulation method, respectively. 3.The method according to claim 1, wherein the excitation currenttime-domain waveform I_(E)(t) is one of a sine wave, a cosine wave, asquare wave or a pulse wave.
 4. The method according to claim 1, whereinthe normalized magnetic nanoparticle signal s(t) is acquired by:s(t)=u _(p)(t)/[I _(E)(t)]^(k) wherein k is a frequency multiplicationnumber of the magnetic nanoparticle response voltage signal u_(p)(t),and k is a positive odd number.
 5. The method according to claim 4,wherein the first mathematical model between the normalized signal peaks_(p) and the magnetic nanoparticle spatial distribution c(r_(n)) isexpressed as:$s_{p} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta V_{n}}}}$wherein A₀(r_(n)) represents the spatial distribution of a non-uniformmagnetic field generated by the excitation coil corresponding to a n-thimaging subunit, p_(R)(r_(n)) represents a magnetic field spatialdistribution generated by the receiving coil corresponding to the n-thimaging subunit, n=1, 2, . . . , N and n represents the n-th imagingsubunit of N imaging subunits, and γ represents a proportionalityconstant related to a frequency of an excitation field, a magneticmoment of a single magnetic particle and a temperature.
 6. Aspatialtemporally coded non-uniform excitation field-based method forperforming a magnetic nanoparticle imaging, comprising: generating, onthe basis of exciting a to-be-reconstructed object through a non-uniformexcitation field H_(E)(r, t) of the method according to claim 1, agradient magnetic field with a field-free region in an imaging spacethrough a pair of direct current coils in an opposite axial direction ora permanent magnet; changing a distribution of the gradient magneticfield through a low-frequency alternating magnetic field generated by alow-frequency alternating current coil, and driving the field-freeregion to scan and traverse an entire imaging space along a set track,so as to obtain M scanning moments and M scanning positions; acquiring anormalized signal peak s_(p)(t_(m)) at a m-th moment thorough the methodaccording to claim 1, wherein m=1, 2, . . . , M; acquiring a voxelfunction ΔV(t_(m), r_(n)) of a response voltage signal of a n-th imagingsubunit at a m-th scanning moment according to the distribution of thegradient magnetic field and the scanned track; constructing a secondmathematical model between the normalized signal peak s_(p)(t_(m)) and amagnetic nanoparticle spatial distribution c(r_(n)) based on thenormalized signal peak s_(p)(t_(m)) at the m-th moment and the voxelfunction ΔV(t_(m), r_(n)) of the response voltage signal at the m-thscanning moment; and solving the second mathematical model to obtain themagnetic nanoparticle spatial distribution c(r_(n)), so as to achievethe magnetic nanoparticle imaging of the to-be-reconstructed object. 7.The method according to claim 6, wherein the second mathematical modelbetween the normalized signal peak s_(p)(t_(m)) and the magneticnanoparticle spatial distribution c(r_(n)) is expressed as:${s_{p}\left( t_{m} \right)} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta{V\left( {t_{m},r_{n}} \right)}}}}$wherein A₀(r_(n)) represents the spatial distribution of a non-uniformmagnetic field generated by the excitation coil corresponding to a n-thimaging subunit, k represents a frequency multiplication number of themagnetic nanoparticle response voltage signal and k is a positive oddnumber, p_(R)(r_(n)) represents a magnetic field spatial distributiongenerated by the receiving coil corresponding to the n-th imagingsubunit, n=1, 2, . . . , N and n represents the n-th imaging subunit ofN imaging subunits, γ represents a proportionality constant related to afrequency of an excitation field, a magnetic moment of a single magneticparticle and a temperature, and t_(m) represents the m-th scanningmoment.
 8. A non-uniform excitation field of a coil array-based methodfor performing a magnetic nanoparticle imaging, comprising: sequentiallyexciting, on the basis of exciting a to-be-reconstructed object througha non-uniform excitation field H_(E)(r, t) of the method according toclaim 1, an imaging space by using a plurality of excitation coils withsame or different axial directions at different positions, so as toconstruct an excitation coil array; simultaneously detecting a magneticnanoparticle response voltage signal by using a plurality of receivingcoils with same or different axial directions at different positions soas to construct a receiving coil array, wherein the plurality ofreceiving coils correspond to the plurality of excitation coils;acquiring a unit current magnetic field spatial function A₀ ^(m)(r_(n))of a m-th excitation coil and a sensitivity spatial function p_(R)^(l)(r_(n)) of a l-th receiving coil, acquiring a volume ΔV_(n) of an-th imaging subunit and n=1, 2, . . . , N, performing a normalizationof a m×l magnetic nanoparticle response voltage signal u_(p)(t), andacquiring a normalized signal peak s_(p) ^(m×l) of a normalized magneticnanoparticle signal s(t) through the method according to claim 1;constructing a third mathematical model between the normalized signalpeak s_(p) ^(m×l) and a magnetic nanoparticle spatial distributionc(r_(n)) based on the normalized signal peak s_(p) ^(m×l) and the volumeΔV_(n) of the imaging subunit; and solving the third mathematical modelto acquire the magnetic nanoparticle spatial distribution c(r_(n)), soas to achieve the magnetic nanoparticle imaging of theto-be-reconstructed object.
 9. The method according to claim 8, whereinthe third mathematical model between the normalized signal peak s_(p)^(m×l) and the magnetic nanoparticle spatial distribution c(r_(n)) isexpressed as:$s_{p}^{m \times l} = {\gamma{\sum\limits_{n = 1}^{N}{\left\lbrack {A_{0}^{m}\left( r_{n} \right)} \right\rbrack^{k}{p_{R}^{l}\left( r_{n} \right)}{c\left( r_{n} \right)}\Delta V_{n}}}}$wherein A₀(r_(n)) represents the spatial distribution of a non-uniformmagnetic field generated by the excitation coil corresponding to a n-thimaging subunit, k represents a frequency multiplication number of themagnetic nanoparticle response voltage signal and k is a positive oddnumber, p_(R)(r_(n)) represents a magnetic field spatial distributiongenerated by the receiving coil corresponding to the n-th imagingsubunit, n=1, 2, . . . , N and n represents the n-th imaging subunit ofN imaging subunits, γ represents a proportionality constant related to afrequency of an excitation field, a magnetic moment of a single magneticparticle and a temperature, m represents the m-th excitation coil and lrepresents the l-th receiving coil.
 10. A non-uniform excitationfield-based system for performing a magnetic nanoparticle imaging, thesystem, based on the method according to claim 1, comprising: a firstmagnetic field excitation module configured to excite ato-be-reconstructed object through a non-uniform excitation fieldH_(E)(r, t); a spatialtemporal separation module configured to perform aspatialtemporal separation of the non-uniform excitation field H_(E)(r,t), so as to obtain a spatial distribution A₀(r) of a non-uniformmagnetic field generated by an excitation coil and an excitation currenttime-domain waveform I_(E)(t); a magnetic field spatial distribution andresponse voltage signal acquisition module configured to acquire, basedon the spatial distribution A₀(r) of the non-uniform magnetic fieldgenerated by the excitation coil and the excitation current time-domainwaveform I_(E)(t), a magnetic field space distribution p_(R)(r)generated by a receiving coil and a magnetic nanoparticle responsevoltage signal u_(p)(t); a normalization module configured to perform anormalization processing on the magnetic nanoparticle response voltagesignal u_(p)(t), so as to obtain a normalized magnetic nanoparticlesignal s(t); a gridding module configured to perform a griddingprocessing on an imaging space of the to-be-reconstructed object, so asto obtain N imaging subunits, wherein a n-th imaging subunit has avolume ΔV_(n) and n=1, 2, . . . , N; a first model construction moduleconfigured to calculate a normalized signal peak s_(p) based on thenormalized magnetic nanoparticle signal s(t) and to construct a firstmathematical model between the normalized signal peak s_(p) and themagnetic nanoparticle spatial distribution c(r_(n)) by combining thevolume ΔV_(n) of the imaging subunit; and a first imaging moduleconfigured to solve the first mathematical model to obtain the magneticnanoparticle spatial distribution c(r_(n)), so as to achieve themagnetic nanoparticle imaging of the to-be-reconstructed object.